Abstract

We present the Twente Optical Perfusion Camera (TOPCam), a novel laser Doppler Perfusion Imager based on CMOS technology. The tissue under investigation is illuminated and the resulting dynamic speckle pattern is recorded with a high speed CMOS camera. Based on an overall analysis of the signal-to-noise ratio of CMOS cameras, we have selected the camera which best fits our requirements. We applied a pixel-by-pixel noise correction to minimize the influence of noise in the perfusion images. We can achieve a frame rate of 0.2 fps for a perfusion image of 128×128 pixels (imaged tissue area of 7×7 cm2) if the data is analyzed online. If the analysis of the data is performed offline, we can achieve a frame rate of 26 fps for a duration of 3.9 seconds. By reducing the imaging size to 128×16 pixels, this frame rate can be achieved for up to half a minute. We show the fast imaging capabilities of the system in order of increasing perfusion frame rate. First the increase of skin perfusion after application of capsicum cream, and the perfusion during an occlusion-reperfusion procedure at the fastest frame rate allowed with online analysis is shown. With the highest frame rate allowed with offline analysis, the skin perfusion revealing the heart beat and the perfusion during an occlusion-reperfusion procedure is presented. Hence we have achieved video rate laser Doppler perfusion imaging.

(a) schematic overview of the signal part (/-hatched) and noise part (×-hatched) for determining the SNR from the power spectrum. (b) comparison between the measured SNR (×) and the SNR (solid line) calculated with Eq. (2).

(a) DC-normalized raw perfusion image (128×128 pixels) of a piece of Delrin of 40 mm in diameter with a hole of 4 mm in diameter, placed on green surgery paper. The hole was filled with IntraLipid 20%. (b) the DC-normalized noise corrected perfusion image of the same sample.

The letters UT (‘University of Twente’) written with capsicum cream on the back of the hand of a volunteer. DC-normalized perfusion image (128×128 pixels) after (a) 3:41 min, (b) 4:32 min, (c) 5:13 min, (d) 7:14 min, (e) 11:36 min, (f) 12:08 min, (g) 13:48 min and (h) 15:13 min (Media 1). (i) Photo of the hand taken with the CMOS camera, the black square indicates the area in which the perfusion is measured.

Continuous recording of 128 × 128 pixel perfusion images in the hand of a healthy subject. (a) the average value of each perfusion image as function of time. (b) – (d) perfusion images at times B, C and D in Fig. (a) and (e) the DC image at times B in Fig. (a) (Media 3).

Continuous recording of 128 × 16 pixel perfusion images in the wrist of a healthy subject. (a) the average value of each perfusion image as function of time. (b) and (c) perfusion images at times B and C in Fig. (a) (Media 4).